Alessandro Aldini Mario Bravetti Alessandra Di Pierro Roberto Gorrieri Chris Hankin Herbert Wiklicky Two Formal Approaches for Approximating Noninterference Properties. 1-43 http://dx.doi.org/10.1007/978-3-540-24631-2_1 2002 conf/fosad/2002 FOSAD db/conf/fosad/fosad2002.html#AldiniBPGHW02